In an electronic control in construction machinery, an electro-hydraulic main control valve with an electro proportional pressure reducing valve (EPPRV) may be used. In conventional construction machinery, during an operation by self-load of an arm or bucket, an operating speed of a work device may be controlled by a meter-out opening area control. In this case, an orifice area curve was designed based on a case that an amount of a working oil supplied to an actuator (arm cylinder, bucket cylinder, etc) is a minimum amount or relatively smaller. Accordingly, during a load operation, not by an operation by self-load, back pressure may be increased to thereby deteriorate fuel efficiency due to pressure loss.